Quench Detection in Insulated, NI, and MI (RE)Ba₂Cu₃O7—x Coils With Superconducting Quench Detectors

We have proposed a quench detection method that uses a low-temperature superconducting quench detector (LTS QD) for rare-earth barium copper oxide (REBCO) coils at 4.2 K. Previous studies demonstrated the quench detection with a LTS QD in a layer-wound REBCO coil. In this study, the quench detection performance of LTS QDs for insulated, no-insulation (NI), and metal-as-insulation (MI) REBCO pancake coils was experimentally compared. An experiment that used a Nb–Ti/Cu–Ni QD installed in insulated, NI, and MI REBCO coils demonstrated a quench detection before a thermal runaway in the coil at 4.2 K and 0–9 T. Nb–Ti/Cu–Ni QD showed slower quench detection in the coils without turn-to-turn insulation. It would be due to the small heat density around the hot spot and large heat exchange between the Nb–Ti/Cu–Ni QD and REBCO coils. In conclusion, this study indicated that the turn-to-turn resistance in the REBCO coil and thermal gap conductance between the coil and LTS QD are key parameters for the design of LTS QDs. Moreover, feasibility of the quench detection with appropriate LTS QDs for the insulated, NI, and MI REBCO pancake coils was demonstrated at 4.2 K.